I went into one of my test sites which has an old Agency theme and had the social icon plugin and I had same problem as you. New settings would not ‘take.’

I dragged the widget out of the footer area and dragged a new one in and made some settings on font size, color, etc. and it worked fine. So try that.

Also, if you are using the icon twice… say in a header and in a sidebar, whatever style settings the the system finds first are the ones it is going to use. So maybe you are using the widget twice on the site?

Anyway, at least try to dump the current one and bring in a new one. My guess is it had something to do with WP 3.9.

This is why I don’t like plugins and their settings and if possible I try to do as much styling in CSS as possible.